MATERIALS AND METHODS

Transcription

1 24 CHAPTER-111 MATERIALS AND METHODS A brief description of the experimental details and methodology followed in this investigation is presented in this chapter. III.1. Characterization of soil acidity in rubber growing soils III.1.1. Collection of soil samples On the basis of NBSS and LUP report (1999), eight major soil series were identified for the study. The soil series selected were Vijayapuram (Vpm), Thrikkannamangal (Tmg), Thiruvanchoor (Tvr), Vazhoor (Vzr), Kunnathur (Ktr), Kangirappally (Kpl), Panachikkad (Pck) and Lahai (Lah). Details of the series are presented in Table 1. Profile sites were located at the type location and pits were taken up to the parent rock. Profiles were examined for morphological characters as per United States Soil Survey Staff (1975) and horizons were identified. Samples were collected horizon-wise from each profile representing the series. The soil samples were processed, dried and sieved through 2 mm sieve and stored for analysis.

2 25 Table-1. Details of the soil series Series Landform Area (ha) Soil Taxonomy Kanjirappally (Kpl) Charnokite Clayey-skeletal,Ustic Kandihumults Thruvanchoor (Tvr) Charnokite Clayey-skeletal,Ustic Kandihumults Vazhoor (Vzr) Charnokite Clayey-skeletal,Ustic Kandihumults Vijayapuram (Vpm) Charnokite Clayey,Ustic Kandihumults Lahai (Lah) Charnokite Clayey,Ustic Kanhaplohumult Kunnathur (Ktr) Khondalite Clayey-skeletal,Ustic Kanhaplohumult Thrikannamangal(Tmg) Khondalite Clayey-skeletal, Ustic Kandihumult Panachikkadu (Pck) Laterite Clayey-skeletal,Ustic Kanhaplohumult III.1.2. Physicochemical properties III Soil reaction (ph) ph of the soil was measured in water, 1M KCl, 0.01M CaCl 2, 1M NaF (Black, 1965; Page et al., 1982). A measured quantity of soil was equilibrated with a specified quantity of solvent viz., water (1:2.5 soil solvent ratio), 1M KCl (1:2.5 soil solvent ratio) 0.01M CaCl 2 (1:2 soil solvent ratio) and 1M NaF (1:50 soil solvent ratio), respectively. The ph of the suspension was determined electrometrically on a direct reading ph meter with combined calomel- glass electrode. Lime potential was obtained by subtracting 1.14 from ph (0.01 M CaCl 2 ).

3 26 III Cation exchange capacity (CEC) Cation exchange capacity (CEC) was estimated using neutral normal ammonium acetate (Black, 1965). III Base saturation per cent Exchangeable Ca and Mg were estimated from the ammonium acetate extract for CEC determination by Atomic Absorption Spectrophotometer (Model GBC, Avanda). Sodium and K were estimated from the same extract by Flame Photometer. Percentage base saturation was calculated using the equation outlined in Jackson (1958). Total exchangeable bases (cmol /kg soil) Base saturation (%) = x 100 Cation exchange capacity (cmol /kg soil) III Particle size analysis Mechanical analysis of the soil samples was done by international pipette method (Jackson, 1958). III Organic carbon (OC) Organic carbon was estimated by Wakley and Black method (Jackson, 1958). III.1.3. Forms of acidity III.1.3.I. Total potential acidity (TPA) (Peech et al., 1962) Soil was leached with a solution containing 0.5N BaCl N tri ethanol amine (TEA) buffered at ph 8.0 ± 0.02 at a soil, solution ratio of 1:10. After shaking for 30 minutes the suspension was kept overnight. This ph corresponds closely with the ph of complete neutralization of hydroxyl- Al compounds. The high concentration of Ba 2+ not only help in the replacement of H + and Al 3+ ions, but also facilitate the hydrolysis of adsorbed Al 3+ ions and the dissociation of acidic R-COOH and R-OH groups, present in the soil organic matter. The acidity resulting from the replacement of

4 27 H + and Al 3+ ions and from the dissociation of acidic groups was neutralized by TEA, a weak base. The excess TEA was estimated by titrating with standard acid (0.2 N HCl) using mixed indicator (methyl red- bromocresol green) to a pink end point. A blank titration was done with the same volume of original extracting solution using the same amount of indicator. Total potential acidity = (B-S) 10 N (cmol/ kg) B= volume of acid consumed by the blank (ml); S= volume of acid consumed by the sample (ml); N= Normality of the acid. III Exchangeable acidity (EA) (Mc Lean, 1965) This method is based on the principle of exchange reaction with the H + and Al 3+ retained on the permanent charges of the adsorbed complex when the soil is treated with neutral salt with negligible buffering properties. Soil was leached with unbuffered 1M KCl in the ratio 1:10 and the replaced exchangeable H and Al forms the exchangeable acidity, and was estimated by titrating the leachate with standard alkali (0.1N NaOH) using phenolphthalein as indicator to a permanent pink end point. III ph dependent acidity (PA) The difference between total potential acidity and exchangeable acidity was taken as the ph dependent acidity. III.1.4. Forms of Al III.I.4.I. Exchangeable Al (Ex. Al) (Mclean 1965) Soil was leached with unbuffered 1M KCl in the ratio 1:10 and the exchangeable Al in the leachate was estimated colorimetrically with aluminon

5 28 (aluminon methos) and the intensity of the colored complex was measured at 535 nm. (Hsu, 1963; Jayman and Sivasubramhaniam, 1974). III.I.4.2. Extractable Al (Extr. Al) (Mclean 1965) Soil was extracted with normal ammonium acetate (ph 4.8) in the ratio 1:10. The soil suspension was equilibrated for 2 hrs and the Al in the extract was estimated colorimetrically by aluminon method. III.I.4.3. Non exchangeable Al (Non Ex.Al) The difference between extractable Al and exchangeable Al forms non- exchangeable Al. III.I.4.4. Soluble Al (Sol. Al) Soil was extracted with 0.01M CaCl 2 (soil solvent ratio 1:2.5) by shaking for 5 minutes and the Al in the extract was estimated colorimetrically by aluminon method. III.I.4.5. Total Al Total Al was determined by HCl-HF method as per Hossner (1996) and estimated by aluminon method. III.I.4.6. Oxalate extractable and dithionate extractable Fe and Al The oxalate Fe and Al (Fe o and Al o ) were determined by extraction with ammonium oxalate in the dark (Mc Keague and Day, 1966) and the dithionite citrate bicarbonate extractable Fe and Al (Fe d and Al d ) were determined by the method of Mehra and Jackson (1960). III.1.5. Total, DTPA extractable and exchangeable Mn and Fe Total Mn and Fe were estimated by HCl extraction (Jackson, 1958). DTPA - extractable Mn and Fe was determined by Lindsay and Norvell (1978). Exchangeable

6 29 Mn and Fe were extracted with neutral normal ammonium acetate in soil solvent ratio of 1:10 and the concentration of Mn in the extract was estimated by Atomic Absorption Spectrophotometer. III.1.6. Effective cation exchange capacity (ECEC) Effective cation exchange capacity was determined by summation of exchangeable Na, K, Ca, Mg and Al in the 1M KCl extract (Reeuwijk, 1993). III.1.7. Aluminium saturation per cent Aluminium saturation percent was expressed as per cent to the ECEC as follows Exchangeable Al Aluminium saturation per cent = x 100 ECEC. III.2. Lime requirement (LR)) of rubber growing soils Surface soil (0 15 cm) samples were collected from Vijayapuram (Vpm), Thrikkannamangal (Tmg), Thiruvanchoor (Tvr), Vazhoor (Vzr), Kunnathur (Ktr), Kangirappally (Kpl), Panachikkad (Pck) and Lahai (Lah) series and were processed, dried and sieved through 2 mm sieve. Lime requirement was estimated by four methods. III.2.1. Shoemaker, Mc Lean and Pratt method (SMP method)(shoemaker et al., 1961) The principle of this method is based on the relationship between soil- buffer ph measurement and lime requirement determined from a soil - lime incubation study. The extracting buffer has an initial ph of 7.5 and is intended for soils with LR>4.5 Mg/ha. With increasing soil ph, the predictive accuracy of SMP decreases. Similarly for soils with high organic matter the decreased reactivity of H + with the buffer causes error in the LR predicted by SMP buffer method.

7 30 In this method, the ph of a soil buffer system was determined after equilibrating 10 ml of buffer (p-nitrophenol - tri ethanolamine-chromate-acetate) with 5.00 g of soil for 30 minutes and the LR values were taken from a table prepared by the authors. III.2.2. Peech method (BaCl 2 -TEA method) (Peech, 1965) Exchange acidity was determined by single equilibrium extraction of soil using one part (4 g) of soil to 25 part (100 ml) of extracting solution (0.5 N BaCl N TEA). A definite aliquot was used for estimating exchange acidity by titrating with 0.2N HCl using mixed indicator (Methyl red and Bromocresol green) and LR was calculated as CaCO 3 pounds per acre using the equation N (B - S) 50, 000. Where N Normality of HCl; B - Blank titre value: S - Sample titre value III.2.3. Adams and Evans method (Adams and Evans, 1962) In this method, the soil was treated with buffer solution containing p- nitro phenol, boric acid, potassium chloride and potassium hydroxide and the ph was determined. Lime requirement was read directly from the appropriate table using soil water and soil buffer system. III.2.4. Exchangeable Al method (Kamprath, 1970) The exchangeable Al value obtained from extraction of soil with unbuffered KCl solution was used to estimate the LR of the soil based on the equation of Kamprath (1970). Lime requirement as CaCO 3 (t ha -1 ) = 1.65 x exchangeable Al in meq/100g soil. III.3. Effect of liming on nutrient availability - Incubation Experiment Soil used for the study was collected from the farm of Rubber Research Institute of India, Kottayam, Kerala State. Lime requirement (LR) of the soil was estimated (6.3 t/ha CaCO 3 ) by Peech method (Peech, 1965). The treatments comprised of four levels of lime, at the rates of 25, 50, 75 and 100 per cent of LR and a no lime control. Powdered shell lime was used as the source of lime. In each treatment the required dose of lime

8 31 was thoroughly mixed with one kg soil and incubated in the laboratory at ambient temperature of C for a period of 90 days. Moisture level was maintained at field capacity throughout the period of incubation. The design of the experiment was CRD with six replications. The physicochemical properties of the initial soil were determined by the standard procedure outlined in Jackson (1958). The incubated soil samples were collected at 15 days intervals up to 90 days and analyzed for organic carbon, available P, K, Ca and Mg (Jackson, 1958). Available P was extracted using Bray II extractant (0.03 N ammonium fluoride in 0.1N HCl) (Bray and Kurtz, 1945) and estimated colorimetrically by molybdenum blue method at 660 nm wavelength. Available K was extracted by Morgan s reagent (sodium acetate + acetic acid buffer of ph 4.8) (Morgan, 1941) and estimated by flame photometer. Calcium and Mg from the Morgan extract was estimated by atomic absorption spectrophotometer. The soil ph (1:2.5, soil: water ratio) was measured by glass electrode method. Exchangeable Al was extracted with 1M KCl and estimated by aluminon method (Hsu, 1963; Jayman and Sivasubramhaniam, 1974) and available Mn, Fe, Cu and Zn by DTPA extractant (Lindsay and Norvell, 1978) were estimated after 90 days of incubation. The individual parameters were statistically analyzed in CRD and the changes over a period of time were estimated by factorial analysis (Snedecor and Cochran, 1967). III.4. Effect of liming on availability of nutrients and growth of rubber seedlings in the nursery A nursery experiment was laid out at the Regional Nursery of the Rubber Board, Perumpulickal in Pathanamthitta District, during season. Lime requirement estimated by Peech method (Peech, 1965) was 8.0 t/ha as CaCO 3. The treatments

9 32 included an absolute control (no lime, no fertilizer), fertilizer and three levels of shell lime viz., 1/3 rd, 2/3 rd and full LR alone and in combination with fertilizer. The design of the experiment was randomized block design with three replications. Nursery beds (4.5 x 1.5 m) were prepared according to nursery practice and powdered shell lime as per the treatments was incorporated by forking. Two weeks after liming germinated rubber seeds were planted (gross 60 seeds and net 30 seeds per plot) in 30 x 30 cm spacing. NPKMg fertilizers (urea, mussoorie rock phosphate, muriate of potash and magnesium sulphate) were applied six weeks after planting and a second dose of urea alone was applied six weeks after the first fertilizer application as per the general fertilizer recommendation. Cultural operations were done according to the nursery practices. Monthly diameter of plants was recorded from March to August The physicochemical properties of the pre treatment soil were determined by the standard procedure (Jackson, 1958). Soil samples (0-30 cm) collected two week after liming and one year after planting were analyzed for organic carbon, available nutrients and ph by standard methods. Leaf samples collected one year after planting were analyzed for total nutrient concentration (Piper, 1942). The data were analyzed statistically. III.5. Effect of liming on translocation of calcium in different plant parts A pot culture experiment was conducted in the glass house of Rubber Research Institute of India with RRII 105 plants to study the effect of liming on uptake and translocation of Ca in different parts of rubber plant. Cement pots of size 60 cm height and 30 cm diameter were filled with 35 kg airdry soil collected from a typical rubber-growing tract. Lime requirement of the soil determined by exchangeable Al method was 4t/ha as CaCO 3. Powdered shell lime

10 33 (quick lime) was the liming material The treatments were lime at the rate of 25, 50, 75 and 100 percent of LR along with fertilizer (NPKMg) at the recommended level, lime at 100 per cent LR alone, fertilizer alone and absolute control. The experiment was laid out in CRD with three replications. Pre-treatment soil sample was analysed for nutrient status (Jackson, 1958). Soil in the pot was thoroughly mixed with lime treatments to a depth of 15 cm. Three weeks after liming budded stumps with one set of whorl were planted and watered regularly. Fertilizers at the recommended level were applied two weeks after planting. Plants were uprooted after four months. Plant parts viz., leaf, stem, petiole and root were separated, dried and weighed and were analyzed for macro and micronutrients (Piper 1942) and soil samples were analyzed for available Ca and ph (Jackson, 1958). III. 6. Comparative evaluation of liming materials on nutrient availability and growth of rubber seedlings in the nursery Nursery experiments were laid out at the Central Nursery of the Rubber Board, Karikkattoor in Pathanamthitta District, Kerala during and seasons. The lime requirement was estimated by Peech method (Peech, 1965) and was 8.0 t/ha as CaCO 3.The treatments included were an absolute control (no lime and no fertilizer), fertilizer alone and three sources of lime viz; powdered shell lime (quick lime), dolomite and of 100 per cent lime requirement with and without fertilizer. The experiment was laid out in a randomized block design with four replications. Nursery beds (4.5 x 1.5 m) were prepared according to nursery practice and powdered liming materials were incorporated by forking. Two weeks after liming, germinated rubber seeds were planted (gross 60 seeds and net 30 seeds per plot) in 30 x 30 cm spacing. NPKMg fertilizers (urea, mussoorie rock phosphate, muriate of potash

11 34 and magnesium sulphate) were applied six weeks after planting and a second dose of urea alone was applied six weeks after the first fertilizer application as per the general fertilizer recommendation. Cultural operations were done according to the nursery practices. Monthly diameter of plants was recorded in January, March and May The physicochemical properties of the pre treatment soil were determined by the standard procedure outlined in Jackson (1958). Soil samples (0-30 cm) collected at the time of planting, before fertilizer application and one year after planting were analyzed for organic carbon, available nutrients and ph by standard methods. The data were analyzed statistically (Snedecor and. Cochran1967). To study the residual effect of liming materials, the experiment was repeated in the same beds in season also. Diameter of the plants was recorded and soil samples (0-30 cm) were collected after one year of planting and analyzed for ph and availability of nutrients. The data were analyzed statistically (Snedecor and. Cochran1967).